Mounting evidence suggests that vitamin B12 may play a role in protecting the brain against Alzheimer’s disease and in reducing the risk of memory loss.

The latest research, published in the Oct. 19 issue of the journal Neurology, followed 271 Finnish residents ages 65 to 79 for seven years. None of the study participants had symptoms of dementia or Alzheimer’s disease at the start of the study.

Researchers from the Karolinska Institutet in Stockholm, Sweden, tested blood samples of the participants for homocysteine, an amino acid associated with vitamin B12, and for levels holotranscobalamin, which is the active portion of B12, according to a statement from the study authors.
High levels of homocysteine in the blood have been associated with a higher risk of Alzheimer’s, but increased levels of B12 can lower homocysteine levels. During the course of the study, 17 participants developed Alzheimer’s disease. And study authors found that for each micromolar increase in homocysteine concentration, the risk of Alzheimer’s disease was increased 16 percent.

They also found that each picomolar (1 picomolar equals 1 million micromolar) increase in concentration of the active form of vitamin B12 reduced risk of the disease by 2 percent.

“Our findings show the need for further research on the role of vitamin B12 as a marker for identifying people who are at an increased risk of Alzheimer’s disease,” said study author Dr. Babak Hooshmand, of the Karolinska Institutet, in a statement. “Low levels of vitamin B12 are surprisingly common in the elderly. However, the few studies that have investigated the usefulness of vitamin B12 supplements to reduce the risk of memory loss have had mixed results.”

A study conducted by Oxford University researchers and released in September looked at the effect of three common B vitamins on homocysteine levels.

For that study, researchers looked for signs of “mild cognitive impairment,” which can be a precursor to Alzheimer’s disease, in the brains of 168 elderly volunteers.

During a two-year period, the volunteers were given a single pill each day containing B12, folate and B6 at 300 times the U.K.’s recommended daily intake of B12, four times the recommended intake of folate and 15 times that of B6.

Brain scans taken before and after the Oxford trial showed that the brains of patients taking the vitamins had shrunk .76 percent each year, while the brains of those in the placebo group shrank by 1.08 percent annually. Brain shrinkage is a symptom of mild cognitive impairment.

Hooshmand, of the Swedish study, says further research is needed to determine whether B12 really does ward off Alzheimer’s disease. In the meantime, the vitamin, which can be found in fish, poultry and other meat products, “should be used solely as a supplement to help protect memory,” Hooshmand added.